Major plot points in chapter 2 in the great gatsby

Your social number is how the government can determine who you are (it’s your identity) and if someone has your social, then they have access to your identity. That means they can go committing crimes with your identity and have access to all your accounts and scamming with your identity and such!
So it’s important to keep it to yourself and the only time you would usually give it out is when your applying for a job.